The objective of the present invention is to provide a practical and economical means to permit straight line backing up of semi-trailer or full trailer vehicle combinations, which operation cannot be accomplished by drivers possessing normal driving skills. The economic advantage offered by the invention is the substantial saving of time at each delivery or pick-up location where straight backing up of the vehicle is desirable or necessary. Also, if a driver mistakenly drives his rig into a narrow dead-end street, this invention will allow the driver to safely back out of his mistake. Another advantage of the invention is that the device embodying the invention can be activated where a tractor-trailer rig is left unattended so that it can only be driven away on a straight path. This will prevent theft of the rig.
Prior U.S. Pat. No. 4,120,514 shows a safety device for tractor-trailers to prevent jackknifing by limiting the articulation angle around the axis of the king pin. The device does not enable backing up of the rig in a straight line. Furthermore, in the prior patent, the safety coupler device is installed directly on the tractor fifth wheel and requires expensive installation procedures which the present invention completely avoids.